1. Field of the Invention
The present invention relates to a method of manufacturing magnetic heads used for writing data on a recording medium and to a magnetic head substructure used for manufacturing the magnetic heads.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction perpendicular to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
For each of the longitudinal magnetic recording system and the perpendicular magnetic recording system, magnetic heads typically used have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate.
For each of the longitudinal and perpendicular magnetic recording systems, the write head incorporates a coil for generating a magnetic field corresponding to data to be written on a recording medium, and a magnetic pole layer for allowing a magnetic flux corresponding to the field generated by the coil to pass therethrough and generating a write magnetic field for writing the data on the recording medium. The pole layer incorporates a track width defining portion and a wide portion, for example. The track width defining portion has an end located in a medium facing surface that faces toward the recording medium. The wide portion is coupled to the other end of the track width defining portion and has a width greater than the width of the track width defining portion. The track width defining portion has a nearly uniform width.
To achieve higher recording density, it is a reduction in track width, that is, a reduction in width of the end face of the pole layer taken in the medium facing surface, and an improvement in writing characteristics that is required for the write head. An improvement in writing characteristics is, for example, an improvement in overwrite property that is a parameter indicating an overwriting capability. The overwrite property is reduced if the track width is reduced. It is therefore required to achieve a better overwrite property as the track width is reduced. Here, the length of the track width defining portion taken in the direction orthogonal to the medium facing surface is called a neck height. The smaller the neck height, the better is the overwrite property.
In the course of manufacturing magnetic heads, a number of magnetic head elements to be the magnetic heads are formed in a single substrate (wafer). The substrate in which the magnetic head elements are formed is cut such that the surface to be the medium facing surfaces appears. This surface is then polished to form the medium facing surfaces.
U.S. Pat. No. 5,742,995 discloses a technique in which a first triangle and a second triangle disposed to be opposite to each other are formed in a wafer and these triangles are used to calculate the height of an MR sensor (that is, the length of the MR sensor taken in the direction orthogonal to the medium facing surface). In this technique the height of the MR sensor is calculated by using the width of the base of the first triangle in the medium facing surface before the wafer is processed (before the wafer is polished), the width of the top of the second triangle in the medium facing surface before the wafer is processed, the width of the base of the first triangle in the medium facing surface after the wafer is polished, and the width of the top of the second triangle in the medium facing surface after the wafer is polished.
U.S. Patent Application Publication US2006/0174475A1 discloses a technique in which, in a substructure used to manufacture magnetic heads, there are provided resistor elements whose resistances vary in accordance with positions of the end faces of the track with defining portions when the medium facing surfaces are formed, and the surface to be the medium facing surfaces are lapped while monitoring the resistances of the MR elements and the resistor elements. In addition, this publication discloses a technique in which, in a substructure used to manufacture magnetic heads, there are provided first resistor elements whose resistances vary in accordance with positions of the end faces of MR elements when the medium facing surfaces are formed, and second resistor elements whose resistances vary in accordance with positions of the end faces of the track with defining portions when the medium facing surfaces are formed, and the surface to be the medium facing surfaces is lapped while monitoring the resistances of the first and second resistor elements.
An example of method of manufacturing magnetic heads will now be described. First, components of a plurality of magnetic heads are formed on a single substrate to fabricate a magnetic head substructure in which a plurality of pre-head portions that will be the magnetic heads later are aligned in a plurality of rows. Next, the magnetic head substructure is cut to fabricate a head aggregate including a single row of the pre-head portions. Next, a surface formed in the head aggregate by cutting the magnetic head substructure is polished (lapped) to form the medium facing surfaces of the pre-head portions that the head aggregate includes. Next, flying rails are formed in the medium facing surfaces. Next, the head aggregate is cut so that the pre-head portions are separated from one another, and the magnetic heads are thereby formed.
An example of method of forming the medium facing surfaces by lapping the head aggregate will now be described. In the method the head aggregate is lapped so that the MR heights of a plurality of pre-head portions are made equal while the resistances of a plurality of MR elements that the head aggregate includes are detected. The MR height is the length of each of the MR elements taken in the direction orthogonal to the medium facing surface.
According to the method of forming the medium facing surfaces as described above, it is possible to form the medium facing surfaces so that the MR heights are of a desired value. As a result, according to the method, a portion of each medium facing surface at which an end of the MR element is exposed is located at a desired position. Furthermore, according to this method, if the angle formed by the medium facing surface with respect to the top surface of the substrate is 90 degrees, a portion of the medium facing surface at which an end face of the track width defining portion is exposed is located at a desired position, too. As a result, the neck height is of a desired value, too.
Conventionally, however, there are cases in which the angle formed by the medium facing surface with respect to the top surface of the substrate deviates from 90 degrees. This is caused by misalignment of the head aggregate and a jig with respect to each other, the jig supporting the head aggregate when the aggregate is lapped. If the angle formed by the medium facing surface with respect to the top surface of the substrate is other than 90 degrees, the portion of the medium facing surface at which the end face of the track width defining portion is exposed deviates from its desired position even though the portion of the medium facing surface at which the end of the MR element is exposed is located at its desired position. As a result, the neck height is of a value other than the desired value.
As described above, if the neck height is of a value other than the desired value, there may be a case in which the track width is of a value other than the desired value, too. As thus described, the conventional problem is that there are some cases in which the portion of the medium facing surface at which the end face of the track width defining portion is exposed deviates from its desired position to thereby cause the track width to be of a value other than the desired value, and as a result, the yield of magnetic heads is reduced.
According to the technique disclosed in U.S. Pat. No. 5,742,995, it is possible to calculate the MR height but it is impossible to solve the above-mentioned problem.
According to the technique disclosed in U.S. Patent Application Publication US2006/0174475A1, it is possible to detect the angle formed by the lapped surface to be the medium facing surfaces with respect to the top surface of the substrate, and to thereby form the medium facing surfaces at desired positions with accuracy.
The following problem arises when the position of the lapped surface is detected while monitoring the resistances of the MR elements or the resistances of the resistor elements disclosed in U.S. Patent Application Publication US2006/0174475A1. The resistance of each MR element or resistor element is inversely proportional to the length of the MR element or resistor element taken in the direction orthogonal to the medium facing surface. Therefore, if this length of the MR element or resistor element is great, a change in resistance of the MR element or resistor element with respect to a change in position of the lapped surface is small. If this length of the MR element or resistor element is reduced, a change in resistance of the MR element or resistor element with respect to a change in position of the lapped surface becomes greater. Therefore, in a case in which there is a great distance between the lapped surface and the target position of the medium facing surfaces, such as a case in which this distance is greater than 1 μm, it is difficult to precisely detect the distance between the lapped surface and the target position of the medium facing surfaces and the angle formed by the lapped surface with respect to the top surface of the substrate. Consequently, if there is a great distance between the lapped surface and the target position of the medium facing surfaces, for example, there may be a case in which the angle formed by the lapped surface with respect to the top surface of the substrate greatly deviates from 90 degrees, and it is impossible to correct this angle later.